Adsorptive attenuation of ferrocyanide from seepage water in landfill clay liners

Abstract

The spent potliner (SPL) landfill liner system provides the primary attenuation mechanism that blocks the leaching of ferrocyanide. If the seepage occurs, however, the off-site leaching potential of ferrocyanide will be enhanced, resulting in contaminant dispersion. In this study, the adsorptive attenuation of ferrocyanide by two common lining materials (kaolinite and montmorillonite) was investigated under various seepage settings, such as influent concentration, liner thickness, and seepage velocity. The attenuation of ferrocyanide through both lining materials was obvious by lowering the maximum concentration and retarding the peak arrival time and was greater than that expected from batch data, likely due to the high mass-volume ratio under seepage condition. In comparison, seepage of ferrocyanide through lining material layer was retarded when (1) influent concentration was halved, (2) liner thickness was 1.5-fold, and (3) seepage velocity was halved. These experimental results strongly support the concentration-specific and rate-limited adsorptive attenuation of ferrocyanide by lining materials during the seepage process. An extended desorption front was observed for all seepage conditions; it was particularly more apparent for montmorillonite with a slow seepage velocity, further supporting that the release of adsorbed ferrocyanide from adsorbent is energetically hysteretic. Among the factors investigated in this study, the greatest retardation of ferrocyanide movement from seepage water was achieved upon doubling liner thickness. Therefore, for the design of a SPL landfill liner to minimize the leaching potential and thus the environmental risk of ferrocyanide, optimization of the liner thickness should be considered foremost.